1. Field of the Invention
The present invention is directed generally to neurostimulation of the vagus nerve, and more particularly to an improved apparatus and method for vagus nerve stimulation therapy using heart rate variability synchronization, patterned electrical pulses inside a pulse burst, and electroencephalogram (“EEG”) based optimization.
2. Description of the Related Art
Vagus nerve stimulation (“VNS”) (for example, VNS Therapy™ by Cyberonics, Inc.) is an FDA-approved method for alleviating treatment-resistant epilepsy and depression.
Vagus nerve stimulation was initially developed and approved by the FDA for the treatment of refractory partial onset epilepsy. Recently, it has been reported that the use of VNS in human patients with epilepsy is associated with an improvement in mood. As a consequence, VNS has also been approved as a treatment for refractory depression (treatment resistant depression).
VNS typically involves implanting a nerve stimulating electrode on the left or right vagus nerve in the neck. The electrode is connected to a subcutaneous pacemaker-like control unit that generates an electrical nerve stimulating signal. A Vagus Nerve Stimulator (“VNS stimulator”) is an example of an implantable stopwatch-sized, pacemaker-like control unit device configured to electrically stimulate the vagus nerve leading to the brain.
Conventional VNS is generally applied every 5 minutes in a 7 second to one minute burst (see FIG. 3A for a portion of an exemplary burst) including a pulse train of uniformly spaced apart pulses having a pulse current amplitude of about 0.5 mA to about 2.0 mA). The pulses are delivered at about 20 Hz to about 50 Hz. Each of the pulses may have a width of about 0.5 milliseconds. VNS is currently approved to treat epileptic seizures and depression when drugs have been ineffective.
Consequently, a need exists for methods of delivering electrical stimulation to the vagus nerve. Further, a need exists for improved electrical signals that increase the efficacy of VNS.